Treatment of tars



Patented Mar. 31, 1936 UNITED STATES PATENT QFFICE TREATllIENT F TARSRichard F. Davis, Chic versal Oil Products ago, 111., assignor to Uni-Company, Chicago, 111., a

Serial No.

7 Claims. (01. 260154) This invention relates more particularly to thetreatment of crude tars such as those obtained in the distillation ofvarious naturally occurring solid carbonaceous materials includingcoals, lignites and shales.

In a more specific sense the invention has reference to an improvedprocess for the extraction and recovery of the tar acids contained invarious crude tars, and distillates or their fractions. The crude tarswhich may be treated by the process of the present invention varyconsiderably in character according to the source of the materialsdistilled, the conditions of distillation such as the temperature andpressure employed and the use of steam or inert gases as carryingagents. The quality of the tars is influenced to a great extent by thetemperature employed. For example, the tars produced from coal attemperatures above 1400 F., and known to the trade as high temperaturetars are generally characterized by lower viscosity, higher aromatichydrocarbon content and lower phenolic content than tars produced atlower temperatures and generally classified as low temperature tars. Ina general way the differentiation on a basis of temperature between hightemperature and low temperature coal tars may also be applied to tarsfrom lignite, peat, shale, etc., although the range of temperaturescorresponding to high and low temperature tars will vary to some extentwith the character of the material distilled.

Tars of the character under discussion consist for the most part ofhydrocarbons of both a straight chain and a cyclic character, theproportions varying with the temperature of distillation, and alsocontain varying quantities of oxygen, nitrogen and sulphur compounds.The oxygen compounds include various compounds of a phenolic andnaphtholic character, the recovery of which constitutes the subject ofthe present invention. The nitrogen compounds include amines andheterocyclic compounds such as pyridine, picolines, lutidines, etc., asWell as some pyrrolle derivatives. The sulphur compounds includeprincipally thiophene and its derivatives and homologs.

The phenolic constituents of tars which frequently comprise substantialpercentages thereof are extremely useful as disinfectants andpreservatives and as intermediates for the manufacture of morecomplicated chemical derivatives such as dyes, explosives, etc., andhence possess a particular commercial value. These compounds are of aweakly acid character (hence the name tar acids) and react with varyingintensity with difierent alkaline reagents to form compounds which maybe generally grouped under the broad term of phenolates. When treatingtars of varying quality with alkali solutions for the extraction of taracids, difliculty is fre- 6 quently encountered in the formation ofextremely persistent emulsions owing possibly to the soap-like characterof the phenolates and the presence of protective colloids. The formationof such emulsions slows up the treating step and 10 decreases thecapacity of equipmentto a large extent.

In one specific embodiment the invention comprises treatment of crudetars containing acidic compounds with aqueous caustic soda ofapproximately 25 Baum strength at temperatures from 140 to 160 F.

I have established as the result of a considerable number of experimentsthat the use of the above mentioned reagent and conditions of treatmentcorrespond to practically complete absence of emulsions when treatingcrude tars for the extraction and recovery of their tar acid content.Baum caustic soda corresponds to a percentage of approximately 18.5 NaOHby weight, 25 and it appears that this particular concentration whenused in an amount corresponding to the neutralization of the acidcontent of the tar and Within the temperature range indicatedconstitutes a solution of a critical concentration in respect to easeand efficiency of operation. The preferred temperature range indicatedabove insures a suificient lowering of the viscosity of the tars withoutunduly increasing the vapor pressure of any volatile constituents whichmay be present. However, in the case of tars containing low boilingcomponents, pressure may be employed to prevent ebullition and theconsequent tendency toward froth production.

The process of the invention may be conducted in either batch orcontinuous apparatus after a titration of a sample of the tar has shownthe approximate amount of alkali necessary for combination with theacidic constituents. As a rule, the most satisfactory results areobtained in the present instance when somewhat more than the equivalentamount of alkali is employed in the extraction, though the necessaryexcess is not large. In batch operations vigorous agitation by means ofpaddles or propellers may be employed to insure eiiective contact ofalkali and tar without danger of emulsion formation. Treatments may alsobe conducted in continuous treating equipment consisting of alternatemixing and settling devices, the preheated tar and caustic solutionbeing pumped into the system at a point preceding a pipe containingbafliing material and the solution of phenolates separated from theremaining tar compounds in a subsequent settler.

I claim as my invention:

1. A process for the treatment of tars containing tar acids to removethe said tar acids and prevent emulsification thereof, which comprisessubjecting the said tars to the action of an aqueous solution of analkali comprising sodium hydroxide of approximately 18 to 20%concentration, at elevated temperatures of from to F. and undersuperatmospheric pressures.

2. A process for the treatment of tar distillates containing tar acidsto remove and separate the latter, which comprises subjecting thedistillate to the action of an aqueous solution of an alkali comprisingsodium hydroxide of approximately 18 to 20% concentration, at anelevated temperature of from 140 to 160 F.

3. A process for the treatment of coal tar containing tar acids toremove the latter, which comprises subjecting the said coal tar to theaction of an aqueous solution of sodium hydroxide of approximately 18 to20% concentration at an elevated temperature of from 140 to 160 F.

4. A process for the treatment of tar fractions containing tar acids toremove the said tar acids and prevent emulsification thereof, whichcomprises subjecting the said tar fractions to the action of an aqueoussolution of sodium hydroxide of approximately 18 to 20% concentration atelevated temperatures of from 140 to 160 F. and under superatmosphericpressures.

5. A process for the treatment of tar fractions containing tar acids toremove and separate the latter, which comprises subjecting the said tarfractions to the action of an aqueous solution of sodium hydroxide ofapproximately 18 to 20% concentration at an elevated temperature of from140 to 160 F.

6. A process forthe treatment of tars containing tar acids to remove andseparate the latter which comprises subjecting said tars at temperatureswithin the range of 140 to 160 F. to the action of an aqueous solutionof caustic soda of approximately 18 to 20% concentration.

'7. A process for separating tar acids from tar fractions containing thesame which comprises treating the tar fractions at from 140 to 160 F.with aqueous caustic soda of approximately 25 Baum strength.

RICHARD F, DAVIS.

